Railway traffic controlling apparatus



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A I ATTORNEY.

Patented Sept. 14, 1937 UNITED STATES RAILWAY TRAFFIC CONTROLLING APPA- RATUS Ronald A. McCann, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa, a corporation of Pennsylvania Application July 22, 1931, Serial No. 552,366

14 Claims.

My invention relates to railway trafiic controlling apparatus for governing traffic over a railway switch, and more particularly to apparatus for insuring reliable operation of the approach or route looking for a railway switch. Other features of my invention will appear as the specifications progress.

The apparatus of my invention is an improvement over that disclosed in the copending applications Serial No. 125,659, filed July 29, 1926, by Herbert A. Wallace for Railway trafiic controlling apparatus; and Serial No. 313,772, filed October 20, 1928, by Howard A. Thompson for Multiple control apparatus.

' I will describe one form of my invention, and will then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form of my invention. Referring to the drawing the reference characters I and 2 designate the trafiic rails of a stretch of railway track which I will call the main track. These rails are divided by the usual insulated rail joints 3 into track sections RT, IT and LT of which the middle track section IT may be termed a detector track section and the two outer track sections RT and LT may be termed approach track sections. Located in the detector section ET is a switch S which when reversed directs trafiic from the main track into a passing siding PS.

Each track section of the main track is provided with a conventional track circuit comprising a source of current such as a battery and a track relay which is designated by the reference character R plus a prefix corresponding to the track section. Track battery 4 for the track section IT is connected across the rails 5 and 6 or the siding PS while these rails, at the fouling point, are connected by wires '3 and 8 to the rails I and 2, respectively, of the main track at the left-hand end of section IT. As the track relay ITR is connected across the rails I and 2 at the right-hand end of section IT, it follows that battery 4, the rails of the siding up to the fouling point, the rails of the main track of the section IT and the track relay iTR. are connected in series. For the approach track sections the track battery is connected across the rails adjacent one end and the track relay across the rails adjacent the opposite end of the section in the customary manner.

Power for operating the apparatus and circuits of my invention may be obtained from any convenient alternating current or direct current source but which is not shown in the figure. In this description I shall consider that the current source supplies direct current and that the relays are all direct current relays. The positive terminal of the source is designated by the reference character BL while the negative terminal is designated by the reference character CL.

The switch S is preferably provided with a switch operating machine SM which is controlled by a switch controlling relay W, and which relay in turn is controlled by the relays BX and GY. The relays 6X and GY are themselves controlled from some remote control point, such for example as a dispatchers ofi'ice, by a remote control system of a convenient type. As the switch machine SM together with its operating circuits form no part of my invention, they are omitted from the drawing for the sake of clearness. It will be understood that the switch machine SM is of one of the standard typesandthat the operating circuits for the switch machine are controlled by the polarized armature of the switch controlling relay W in accordance with the usual practice. That is to say, when the relay W is energized with current of a normal polarity the switch machine SM positions the switch S for trafiic on the main track, While when the relay W is energized with current of a reverse polarity the switch S is positioned for trafiic to and from the siding PS. The relay W is of the direct current polarized type wherein the polarized armature will remain in the position to which it was last moved whenever its Winding becomes deenergized, and sufiicient contact pressure will be maintained by the armature with its contacts to hold properly closed the operating circuit passing therethrough.

The circuit for energizing the relay W with current of normal polarity starts at the positive terminal BL and includes the back contact of armature 9 of relay fiY, front contact of armature IE3 of relay 6X, winding of relay W, front contact of armature II of a route locking relay RMR. to be described later, wire I2, front contact of armature I3 of a second route locking relay LMR to be described later also, front contact of armature it of the track relay ITR of the detector track section IT, front contact of armature I5 of relay 6X, back contact of armature I6 of relay SY and to the negative terminal CL. With relay 6! energized and its armatures 9 and It brought into engagement with front contacts and the relay 6X deenergized so that its armatures I and I engage back contacts then the current supplied to the relay W by the above circuit is of a reverse polarity. The control system for selectively controlling the relays SX and 68! forms no part of my invention and is not shown in the drawing. It will be understood that these relays may be controlled by some one of the remote control systerms which are in general use. As a matter of fact instead of making use of relays SK and tY as the means for controlling the current supplied to the switch controlling relay W this circuit may be controlled by circuit controllers operated by a lever of an interlocking machine. It follows then, that the current supplied to the relay W is of normal or reverse polarity according as relay BX or BY is selected, or if a lever is the controlling element according as that lever is in a normal or a reverse position, and, consequently, the switch S will occupy its normal or reverse position according to the relay selected or according to the position of the controlling lever. It will be noted that the circuit for the relay W cannot be closed unless the detector track section IT is unoccupied and unless the route locking relays RMR and LMR are both energized.

Trafiic moving from the right to the left is controlled by the signals L2A and L2B, and will be spoken of in this description as Westbound trafiic. Traffic moving from the left to the right on the main track is controlled by the signal RZA, while trafiic moving from the siding PS to the right is controlled by the signal B2B. Traffic moving from the left to the right will be spoken of in this description as eastbound traffic. These signals may be of any standard type and are here shown as semaphore signals each capable of displaying a stop or clear indication. The operating circuit for each signal is controlled by a signal controlling relay designated in the drawing by the reference character H with a prefix corresponding to the signal. These operating circuits will be readily understood by an inspection of the drawing and it is thought that it is sufiicient to say that with a signal controlling relay H energized the operating circuit for the associated signal is closed to clear that signal. The system for controlling the signal controlling relays also forms no part of my invention and is omitted from the figure. It will be understood that these signal controlling relays may be controlled by the same remote control system that controls the relay SK and BY and that the energizing of the signal controlling relay is governed jointly by the remote control system and by traffic conditons in advance of the signal in accordance with standard practice.

An indicating relay RGP is associated with the eastbound signals RZA and B2B. This relay RGP is normally energized by a circuit from posi tive terminal BL through a controller I! operated by the signal B2B as indicated by a dotted line and which controller is closed only when the signal B2B indicates stop, circuit controller l8 operated by the mechanism of signal RZA and closed only when that signal is in its stop position, winding of relay RGP and to the negative terminal CL. An indicating relay LGP is associated with signals L2A and LZB and is energized by a circuit including the controllers l9 and 20 operated at the signals LZA and L2B, respectively, and which controllers are closed only when the associated signal occupies its stop position. It follows then that these indicating relays RGP and LG? are both normally energized and become deenergized whenever an associated signal is cleared to permit a trafiic movement over the switch S.

The apparatus includes an eastbound route locking relay RMR and a westbound route locking relay LMR. The relay RMR is provided with a normally closed energizing circuit that passes from the positive terminal BL through the front contact of armature 2! of the relay RGP, wire 22, front contact of armature 23 of the track relay RTR for the approach track section RT, contact 24 of circuit controller L connected to and operated by the switch S and which contact is closed when the switch is set for trafiic on the main track, wire 25, front contact of armature 26 of the detector track relay ITR, wire 21, winding of relay RMR and to the negative terminal CL. This relay is provided with a stick circuit that branches from wire 22 and includes a wire 28, front contact of its own armature 29 and the winding of the relay to the negative terminal CL. A pick-up circuit is provided for the relay RMR that branches from the wire 22 along wires 28 and 33, front contact of armature 32 of a slow-acting relay ITZ when that relay is energized as will be described later, wire 3|, back contact of armature 30 of the track relay LTR when that relay is deenergized, wire 25, front contact of armature 26 of relay ITR, wire 21 and winding of relay RMR to the negative terminal CL. The relay RMR can be energized by still another circuit that is the same as before traced from positive terminal BL up to the wire 33, thence along wire 36, front contact of armature 35 of a time element device ITE to be described later, wires 34 and 25 and then as before pointed out to the winding of the relay RMR.

The route locking relay LMR is provided with a circuit network similar to that described for the relay RMR. The normal energizing circuit for the relay LMR. passes from the positive terminal BL through the front contact of armature 31 of relay LGP, wire 38, front contact of armature 39 of the track relay LTR for the approach track section LT, wire 43, front contact 4| of the detector track relay lTR, winding of relay LMR. and to the negative terminal CL. A stick circuit for relay LMR branches from the wire 38 and extends along the wire 42 and the front contact of its own armature 43 to the winding of the relay and to the negative terminal CL. A pick-up circuit extends from the wire 38 along wires 42 and 41, front contact of armature 46 of the slowacting relay lTZ when that relay is energized, wire 45, back contact of armature 44 of the track relay RTR when that relay is deenergized, wire 48, front contact of armature 4| and the winding of relay LMR to the negative terminal CL. The relay LMR also can be energized by a circuit that is the same as that just traced up to the wire 41, thence through the front contact of armature 49 of the time element device ITE, wire 48 to the wire 48 and then as before pointed out to the Winding of the relay LMR. When the switch S is set for the siding and the contact 24 of the controller L moved to its reverse position, that is, to the lower position in the drawing, a by-pass circuit is closed around the back contact of the armature 44 of relay RTR. This by-pass circuit extends from wire along wire 5!, contact 24 and wire 50 to the wire 40. Thus each of these route locking relays is normally energized and is deenergized whenever a signal governing traflic in the same direction as that with which the relay is associated is cleared. When the route locking relay is energized it closes a contact in the circuit to the switch controlling relay W as previously pointed out and when it is deenergized the circuit to the switch controlling relay is opened to prevent operation of the switch S. The function of the circuit network associated with each route locking relay will be fully pointed out when the operation of my system is described.

The slow-acting relay lTZ is provided with an energizing circuit that passes from the positive terminal BL through the back contact of armature 52 of the detector track relay ITR when that relay is deenergized, resistance 53, Winding of re- 1 traffic.

lay [T2 and to the negative terminal CL. Once the relay iTZ is picked up the resistance 53 is shunted by a path through a front contact of its own armature d. As is well-known the pick-up period of a direct current relay is in a measure proportional to the value of the current applied to its winding. With a given source of current the value of the resistance 53 will thus determine the time required to magnetically saturate the cores of the relay lTZ sufficiently to lift the armature of the relay into engagement with its front contacts, and thus it follows that the pick-up period of the relay iTZ is in this case determined by the resistance 53 and can be made long or short by selecting the relative value of the resistance. I prefer to provide the resistance 53 with such a value that the pick-up period of the relay lTZ is relatively long, say five seconds. In direct current relays provided with slow-releasing characteristics the release period is increased when the energizing current is increased. The relay HTZ is provided with slow-release characteristics and thus the shunting of resistance 53 as the relay is picked up establishes full energization of the relay and thereby insures a full release period for the relay. Thus I have provided a combination whereby the relay lTZ will not pick up its armature until some time after its energizing circuit is closed and then when once the relay is picked up its energization is materially increased so that the relay has a relatively long release period.

The apparatus also includes a time element device l'IE. This time element device may take different forms several of which are well-known to the art. In this instance I prefer to employ a time element device of the relay type. Such relays are in general use and need not be described further than to say that this relay will not operate its armatures for some predetermined interval of time after the energizing circuit for its winding is closed. In this description I shall speak of the predetermined time interval that the winding of the relay lTE must be energized before its armatures 35 and M are operating as being five minutes. It will, of course, be understood that this time interval can be made to suit the local conditions. The relay iTE is provided with two energizing circuits one of which is associated with eastbound traffic and the other with westbound The circuit associated with eastbound trafiic starts at the positive terminal BL at the armature M of relay RGP and includes the wire 28, back contact of armature 29 of the relay RMR, wire 5?, front contact of armature 55 of the track relay l'IR, winding of the relay ITE and to the negative terminal CL. The circuit associated with westbound traffic starts at the positive terminal BL at armature Bl of relay LGP and includes wires 38 and 4 2, back contact of armature 43 of the relay LMR, wires 55 and 5'1, front contact of armature 55 and winding of relay l TE to the negative terminal CL. It follows that whenever route locking relay is deenergized and the associated indicating relay is energized a circuit is closed to the winding of the time element relay lTE.

In describing the operation of my invention I shall assume that the parts of the apparatus are in the position in which they are shown in the drawing and that an eastbound train is to be advanced over the switch on the main track. The remote control system will first function to select the relay 6X so as to position the switch S for the main track. Then as the signal controlling relay RiAI-I is energized the signal RZA is cleared. The clearing of signal RZA deenergizes the relay RGP to open the circuit to the route locking relay RMR, at the armature 2!. With relay RMR once deenergized no movement of the switch can take place due to the fact that the control circuit for the relay W is now open at the armature ll of the route locking relay RMR. As the eastbound train advances into the approach track section RT and shunts the track relay RTR the energizing circuit to the relay RMR. is also opened at the armature 23. When the eastbound train enters the detector track section HT and shunts the relay lTR the signal R2A will, of course, be set at stop by the customary control circuit not disclosed here-in, and the circuit to the relay RGP closed thereby to r'eenergize that relay. Although the relay RGP is now picked up no circuit is completed to the route locking relay RMR as long as the train occupies the detector track section as all pick-up circuits leading to the relay RMR are controlled by the front contact of armature it of the detector track relay :ITR. When the eastbound train advances east through the sections RT and lT and vacates these sections the relays RTR and ETR will be in turn picked up and the normal energizing circuit to the route locking relay RMR. closed to reenergize that relay. That is to say that as soon as the eastbound train vacates the detector track section iT the route locking is released and the switch S is free to be operated.

As the detector track circuit is shunted by the eastbound train and the relay ITR deenergized, the circuit to the slow-acting relay iTZ is closed and after a period which we have taken as five seconds, it lifts its armatures into engagement with the front contacts. When the eastbound train shunts the westbound approach track section LT, a. pick-up circuit is established for the relay RMR. which is not completed, however, until the rear of the train vacates the section lT and the track relay lTR is reenergized. Although this pick-up circuit for relay RMR was previously pointed out it is thought that it might be well to again trace it from positive terminal BL through armature ill, wires 28 and 33, armature 32, wire 35, back contact of armature 38, front contact of armature 26, wire 27!, winding of relay RMR and to the negative terminal CL. This circuit will be closed only during the release period of the relay lTZ due to the fact that as the track relay ETR picks up to close this circuit for the relay RMR at the front contact of armature 2i; it also opens the energizing circuit to the relay ETZ at the back contact of the armature 52. In case a second eastbound train has entered the approach track section RT before the first eastbound train vacates the section lT, then when the first train vacates section lT and enters section LT the route locking relay RMR would be reenergized and the route locking released by this pick-up circuit just traced. It is understood, of course, that the signal R2A is set at stop and relay RGP energized behind the first train. Although this pick-up circuit for relay RMR is closed only during the release period of relay lTZ, the relay RMR once energized will be retained energized by its stick circuit.

In the case where the switch is reversed and the signal B2B cleared for a train to advance east from the siding PS the circuit to the route locking relay RMR is opened at the contact 24 as the switch is positioned for the siding, and also by the relay RG1? as the signal B2B is cleared. As the train advances east from the siding and signal RZB set at its stop position the normal circuit for energizing relay RMR still will be held open at the contact 24 and the route locking still retained effective. As this train enters the detector track section and shunts the relay ITR the energizing circuit to the slowacting relay lTZ is closed and after its pick-up period of five seconds the armature 32 engages the front contact that is included in the pick-up circuit previously traced to the relay RMR. As

this train enters the track section LT and vacates the section IT this pick-up circuit for relay RMR is completed and that relay reenergized after which it is retained energized by its stick circuit, and thus the switch S is released from the route locking.

The operation of the route looking for a westbound train is similar to that described for eastbound traffic except when a movement is made into the siding. As the switch S is set for the siding the contact 24 is moved to its reverse position. As a west bound train occupies the detector track section the relay ITZ is energized and picked up at the end of its five second pickup period and a circuit is formed from the positive terminal BL through the armature 37 of relay LGP, wires 38, 42 and 47, front contact of armature 36 of relay lTZ, wires 45 and 51, contact 24, wires 58 and M, front contact of armature 4! when relay ITR is picked up, winding of relay LMR and to the negative terminal CL. It follows that as the Westbound train moves into the siding and vacates the detector track section IT so that relay ITR is picked up an energizing circuit to the route locking relay LMR is closed during the release period of the relay ITZ. With relay LMR. once picked up it is held energized by its stick circuit and thus the route looking for the switch S is released as soon as this westbound train moving into the siding vacates the section lT. It is to be noted that an eastbound train entering the approach track section LT and shunting the track relay LTR does not deenergize the westbound route locking relay LMR. Under this traffic condition the relay LMR is retained energized by its stick circuit due to the fact that the signal indicating relay LGP will be retained energized. In like manner a westbound train entering the approach track section RT will not deencrgize the eastbound route locking relay RMR as its stick circuit is completed at the front contact of the armature 2| of the signal indicating relay RGP.

The relatively long pick-up period provided for the relay ITZ makes this relay practically immune from momentary interruptions of the detector track circuit as it requires that the detector track relay be opened for a definite period of time before it will function to set in motion the releasing of the route locking. This insures against the possibility of the release of the route looking for a given direction of trafiic movement by a momentary shunt of the detector track circuit at a time when the approach track section for the opposite direction is occupied. Assume for example, that the switch S is set for the siding and a westbound train is approaching in the track section LT while at the same timean eastbound train occupies the section RT to the rear of the signal RZA. A momentary shunt of the detector track section IT for any cause whatsoever will close the energizing circuit to the relay ITZ and if that relay should immediately pick up the route locking would be released when the momentary shunt on the detector track section is removed and its track relay reenergized. The shunting of the detector track section will set the westbound signal at stop and the relay LGP will become reenergized and if the relay ITZ is now up the pick-up circuit for the relay LMR is closed during the release period of the relay ITZ. Such a false release of the route locking where the switch is controlled by a remote control system may result in the dispatcher acting to change the position of the switch in the face of an approaching train. With the relay I TZ requiring a pick-up period of some definite length, say five seconds, then any momentary shunting of the detector track section will not result in a release of a route locking. By the shunting of the resistance 53 as the relay ITZ is picked up so that the energization of this relay is materially increased a slow-release period is readily provided for the relay iTZ that is of sufiicient duration to insure reliable operation of the route locking relay when that relay is being reenergized by a circuit that is closed only during the release period of the relay lTZ.

The function of the time element relay ITE is to provide the release of the route locking when a signal is returned to the stop position before it is accepted by a train. As previously pointed out when the signal RZA is cleared, the relay RMR is deenergized. Should the signal REA be now set at stop by the deenergizing of the signal controlling relay RAZH by the dispatcher, or if deenergized otherwise, without an eastbound train having advanced past the signal and while the train still occupies the approach track section RT the energizing circuit associated with eastbound traffic for the relay lTE is completed and after a predetermined interval, which in this discussion we have assumed to be five minutes, the armature 35 engages its front contact. As the armature 35 engages its front contact then an energizing circuit for the relay RMR can be traced from positive terminal BL through armature 2|, wires 28, 33 and 36, armature 35, wires 34 and 25, armature 26, wire El, winding of the relay RMR, and to the negative terminal CL. It follows that with a signal cleared and the route locking rendered eflective the time element device ITE will release the route looking after a predetermined interval in the event the signal is set at stop before the train has accepted the signal, the time interval being made of such duration that an approaching train will have come to a stop to the rear of the signal or will be over the switch and gone before the switch can be moved. The relay lTE functions to release the route locking relay LMR in connection with westbound trafiic in the same manner as has just been described in connection with eastbound traffic where the route locking relay RMR is reenergized.

Such a system as here disclosed provides a normal route locking circuit that becomes effective as soon as a signal is cleared for the route and which will be released as soon as the track circuits involved are vacated. The route locking circuit being controlled by front contacts of the track relays a momentary shunting of the detector track section will not release the route locking. As the clearing of the signal rendered the route looking effective the loss of shunt of the approach track section will also not effect a release of the route locking. As a matter of fact a simultaneous combination of a loss of shunt for the approach track section and a shunting of the detector track section will not bring about the release of the route locking circuit. Under trafilc conditions that prevent the normal route locking circuit from functioning to release the route locking relay a pick-up circuit controlled by a slow-acting relay operates to reenergize the route locking relay and this slow-acting relay is also immune from false operation resulting from a momentary shunting of the detector track section. The utility of such a route locking circuit will be apparent to all familiar with the art.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track .including an approach track section and a detector track section, a switch leading from the detector track section, a signal to govern the movement of trafiic from the approach track section into the detector track section, a track relay for each said track section, an indicating relay energized when the signal is at stop position, a route locking relay to control the operation of the switch arranged to permit operation of said switch when energized and to prevent operation of the switch when deenergized, and a circuit to energize said route locking relay including a front contact of the indicating relay and a front contact of each said track relay.

2. In combination, a stretch of railway including a railway switch and divided into a track section adjacent the switch and a track section in advance of the switch, a signal to govern trafiic over the switch, a route locking relay to control the operation of the switch arranged to permit the operation of the switch when energized and to prevent the operation of the switch when deenergized, means responsive to the clearing of the signal to deenergize said relay, a normally deenergized slow-acting relay, circuit means responsive to a train occupying the track section adjacent the switch to energize said slow-acting relay arranged to pick up said relay only after the energizing circuit has been closed a definite period of time, and a circuit including a contact closed only when the track section in advance of the switch is occupied and including also a front contact of the slow-acting relay to at times energize the route locking relay.

3. In combination, a stretch of railway including a switch and divided into a track section adjacent the switch and a track section in advance of the switch, a signal to govern traflic through the stretch, a track relay for each section responsive to trafiic conditions of the section, a route locking relay to control the operation of the switch arranged to permit operation of the switch when energized and to prevent operation of the switch when deenergized, means to deenergize said route locking relay when the signal is cleared, a normally deenergized relay, a circuit to energize said relay when a train occupies the track section adjacent the switch arranged to pick up said relay only after the relay has been energized a given interval of time; and another circuit means including a front contact of the track relay for the section adjacent the switch, a back contact of the track relay for the section in advance of the switch and a front contact of the normally deenergized relay to energize the route locking relay.

4. In combination, a stretch of railway including a switch and divided into a track section adjacent the switch and a track section in advance of the switch, a relay to control the operation of the switch arranged to permit operation of the switch when energized and to prevent operation of the switch when deenergized, an electroresponsive device arranged to operate a contact when energized, a circuit means rendered eifective to energize said device only when the track section adjacent the switch is occupied and arranged to cause operation of the contacts of said device a given interval of time after said device becomes energized, and a circuit closed only when the track section in advance of the switch is occupied and including also a contact of said electroresponsive device to at times energize the said relay.

5. In combination, a stretch of railway including a switch and divided into a track section adjacent the switch and a track section in advance of the switch, a first relay to control the operation of the switch arranged to permit operation of the switch when energized and to prevent operation of the switch when deenergized, a second relay, a circuit closed only when the track section adjacent the switch is occupied to energize the second relay and arranged to cause said relay to be picked up a given interval of time after said circuit is closed, and another circuit closed only when the track section in advance of the switch is occupied and the second relay is picked up to energize said first relay and thereby permit operation of said switch.

6. In combination, a stretch of railway arranged to provide diiierent trafiic routes and including a first and a second track section, a first relay to control the selecting of said trafiic routes arranged to permit a change of routes when energized and to prevent a change of the route when deenergized, a second relay, a circuit closed in response to a train occupying the first track section to energize the second relay and arranged to cause said relay to be picked up a given interval of time after said circuit is closed,

and another circuit closed by the train vacating the first track section and occupying the second track section and by the picking up of the said second relay to energize said first relay and thereby permit a change in the routes.

7. In combination, a stretch of railway including a detector track section, a switch leading from the detector track section, a route locking relay to control the operation of said switch arranged to permit operation of the switch when energized and to prevent operation of the switch when deenergized, means to at times deenergize said route locking relay, a normally deenergized slow-release relay, a circuit effective to energize said slow-release relay when a trainoccupies said detector track section arranged to pick up said relay only after said circuit has been closed a definite period of time, means adapted to increase the energization of said slow-release relay after it is picked up to thereby insure a full I switch when energized and to prevent operation of the switch when deenergized, means to deenergize at times said route locking relay, a normally deenergized slow-release relay, circuit means including a resistance controlled by said track relay to energize said slow-release relay effective to pick up said relay only after said track relay has been shunted a given period of time, means to shunt said resistance and thereby insure a full release period for said slow-release relay when said relay is once picked up, and a circuit including a front contact of said track relay eifective to energize said route locking relay during the release period of said slow-release relay.

9. In combination, a stretch of railway track divided into a detector track section and two approach track sections including one adjacent each end of said detector track section, a track 30 switch leading from the detector track section,

a signal for governing the movement of trafiic from one approach track section into the detector track section, a track relay for the detector track section, a slow pick-up relay controlled by said track relay, a locking relay for said switch; a

plurality of circuits for said locking relay, including a pick-up circuit closed only when said one approach track section is unoccupied, a sec ond pick-up circuit controlled by said slow pickup relay and closed only when the other approach track section is occupied, and a stick circuit including a front contact of the locking relay, each of said circuits also including a contact closed only when said signal indicates stop; and means controlled by said locking relay for controlling said switch.

10. In combination, a stretch of railway track divided into a detector track section and two approach track sections including one adjacent each end of said detector track section, a track switch leading from the detector track section, a signal for each direction for governing the movement of traffic from the adjacent approach track section into the detector track section, a track relay for the detector track section, a slow pick-up relay controlled by said track relay, a locking relay for each direction for said switch; a plurality of circuits for each locking relay, including a pick-up circuit closed only when the approach track section for the corresponding direction is unoccupied, a second pick-up circuit controlled by said slow pick-up relay and closed only when the approach track section for the opposite direction is occupied, and a stick circuit including a front contact of such locking relay, each of such circuits also including a contact closed only when the signal for the corresponding direction indicates stop; and means controlled by said locking relays for controlling said switch.

11. In combination, a stretch of railway track divided into a detector track section and two approach track sectionsincluding one adjacent each end of said detector track section, a track switch leading from the detector track section, a signal for governing the movement of traffic from one approach track section into the detector track section, a track relay for the detector track section, a slow pick-up relay controlled by said track relay, a locking relay for said switch; a plurality of circuits for said locking relay, including a pick-up circuit closed only when said one approach track section is unoccupied, a second pick-up circuit controlled by said slow pickup relay and closed only when the other approach track section is occupied, a third pickup circuit closed if the locking relay remains deenergized for more than a predetermined time interval, and a stick circuit including a front contact of the locking relay, each of said circuits also including a contact closed only when the signal indicates stop; and means controlled by said locking relay for controlling said switch.

12. In combination, a stretch of railway track divided into a detector track section and two approach track sections including one adjacent each end of said detector track section, a track switch leading from the detector track section, a signal for governing the movement of traffic from one approach track section into the detector track .a

section, a track relay for the detector track section, a slow-pick-up relay controlled by said track relay, a locking relay for said switch; a plurality of circuits for said locking relay, in

cluding a pick-up circuit closed only when said.

one approach track section is unoccupied, a sec- 1 and pick-up circuit controlled by said slow pickup relay and closed only when the other approach track section is occupied, and a stick circuit including a front contact of the locking relay, each of said circuits also including a contact closed only when said signal indicates stop, and each of said circuits except the stick circuit also including a front contact of said track relay; and means controlled by said locking relay for controlling said switch.

13. In combination, a stretch of railway track divided into a detector track section and two approach track sections including one adjacent each end of said detector track section, a trackswitch leading from the detector track section, a signal for governing the movement of traffic from one approach track section into the detector track section, a locking relay for said switch, a

pick-up circuit for said locking relay closed only when the signal indicates stop and said one approach track section is unoccupied, a second pick-up circuit for said locking relay closed in response to the movement of a train completely out of the detector track section into the other approach track section, a stick circuit for said locking relay closed when said relay .is picked up and the signal is at stop, and means controlled by said locking relay for controlling said switch.

14. In combination, a stretch of railway track divided into a detector track section and two approach track sections including one adjacent each end of said detector track section, a. track switch leading from the detector track section, a signal for governing the movement of traffic from one approach track section into the detector track section, a locking relay for said switch, a pick-up circuit for said locking relay closed only when the signal indicates stop and said one approach section is unoccupied, a second pick-up circuit for said locking relay closed in response to the movement of a train completely out of the detector track section into the other approach track section, a third pick-up circuit for saidlocking relay closed when said signal indicates stop if the locking relay remains deenergized for more than a predetermined time interval, a stick circuit for said locking relay closed when said locking relay is picked up and the signal indicates stop, and means controlled by said locking relay for controlling said switch.

RONALD A, MoCANN. 

